1. Field of Invention
The present invention relates to an improved martensitic stainless steel, which can be processed by cold pressing and exhibits a high strength when heat treated.
2. State of the Art
Certain kinds of austenitic, ferritic and martensitic stainless steels are used for production of screws by cold pressing or heading. Some steelmarks are standardized in JIS, and as the martensitic stainless steel, SUS 410 is the most popular one.
In order to enhancing the efficiency of screwing, particularly in the fields of building and automobile production, it is getting more popular to use self-tapping screws which require prepared hole but no tapping because they tap when drove, and self-drilling screws which can even prepare holes simultaneously with tapping. To enable the self-tapping and the self-drilling, the screw should have a high mechanical strength. Conventional steels such as the above mentioned SUS 410 are not competent to these types of use.
Accordingly, there has been a demand for stainless steels of high strength. In general, however, it is a common knowledge that increase of mechanical strength of stainless steels inevitably impairs workability and corrosion resistance thereof.